Method of tipping-off the exhaust tube of an electric lamp,and a baseless single-ended incandescent lamp produced by such method



United. States Patent [72] Inventor William L. Brundige [56] ReferencesCited I grldwell, NJ. UNITED STATES PATENTS P 2 2 2 64 .v 9 [22] F e n969 3.16 ,50 1 '/l9 L H erbeek 33 /144 [45] "Patented Dec-29, 1970PrunaryExammerRaymond F. Hossfeld [73] Assignee Westinghouse ElectricCorporation Attorneys-A. T. Stratton. W. D. Palmer and D. S. BulezaPittsburgh, Pa.

l is van ABSTRACT: The exhaust tube of an electric lamp is tipped off ata point which is recessed within the stem cavity by fabricating theenvelope and stem from infrared-radiation transmitting glass and byfabricating the exhaust tube from inflared-radiation absorbing glass.The exhaust tube is tipped off within the stem cavity by a focused beamof infrared-radiation [54] gfi g fg g that is generated by an externalsource and passes through the intervening portions of the lamp envelopeand stem tube. S1NGLE-ENDED INCANDESCENT LAMP since the ti ff 0 h d trnonucnn av sucn METHOD e 8 CI i 2D in n fires. It can be performed in apressurized chamber. T1115, m

ams, I 8 a turn, facilitates the manufacture of incandescent lamps con-[-52] [1.8. CI. 313/318, taining a till gas at supra-atmosphericpressure.

, 220/22; 316/19: 339/ 144 The recessed tipping-off of the exhaust tubealso provides a [51] Int. Cl. 1-101j 5/50 practical single-endedbaseless incandescent lamp wherein the [50] Field olSearch 220/22; leadwires are electrically connected to side and end contacts that arefastened directly to the sealed neck of the envelope.

- PATENTEDUEMQIQYG 3551.725

FIG.2.

INFRARED ENERGY SOURCE WITNESSES NTOR William L. Brundige METHOD OFTlPPING-OFF THE EXHAUST TUBE OF AN ELECTRIC LAMP, AND A BASELESSSINGLE-ENDED INCANDESCENT LAMP PRODUCED BY SUCH METHOD BACKGROUND OF THEINVENTION tipoff.

2. Description of the Prior Art I Conventional gas-filled incandescentlamps are charged to a 4 I pressure below atmospheric pressure due tothe face that the exhaust ti'p blows out" and ruptures while in softenedcondition when a high-fill-gas pressure is employed. The manufacturingcomplications or pressure tipping or reducing the internal gas pressureby cooling the lamp and then tipping-off the exhaust tube with gas firesmake these solutions impractical. As a result, the exhaust tubes of suchlamps are customarily tipped off at a point beyond the sealed neck ofthe envelope. The protruding tip is protectively enclosed by a hollowbase member having a metal shell which is secured by cement to theenvelope neck. Such metal base members are quite expens'ive andmaterially increase the manufacturing costof the lamp. v

'Because of the aforementioned problems it has heretofore been verydifficult, if not impossible from a practical standpoint, to tipoff theexhaust tube at a point which is recessed deeply enough within the stemcavity to provide the degree of protection requisite for a baselessincandescent lamp. While baseless incandescent lamps are per se knowninthe art, they either completely eliminate the exhaust'tu be or employan end cap which protectively enclosesthe protruding fragile .tip of theexhaust tube. Baseless lamps in which the exhaust tube is omitted aredisclosed in U.S. Pat. Nos. 1,946,104 issued Feb. '6, 1934 to T. Oharaet all and U.S. Pat. No. 2,327,622 issued -Aug. 24, 1943, to P. H.Craig. Baseless incandescent lamps having protectively cappedexhaust-tube tips are disclosed in U.S. Pat. No. 3,162,502 issued Dec.22, 1964 to L. H. Verbeek and Canadian Pat. No. 696,040 issued Oct.13,1964 to the same inventor.

SUMMARY OF THE INVENTION It is accordingly the general object of thepresent invention toprovide a practical and inexpensive means fortipping-off the vitreous exhaust tube of an electric lamp at a pointwhich is recessed within a reentrant cavity that is formed at the end ofthe lamp envelope either by the stem tube or by the end wall of theenvelope itself.

Another object is the provision of a method for tipping-off the exhausttube of an electric lamp without the use of gas fires and therebyfacilitating the manufacture of lamps that ing portions of the envelopeand stem tub'e from a point located outside of the lamp being processed.The infrared radiation can be generated by an incandescent coil ofoxidation-resistant material but it is preferably generated by a compactquartz halogen-type incandescent lamp that is fitted with as'uitablerefl'ector which focuses the infrared energy onto the exhausttube.

A single-ended high-pressure baseless incandescent lamp having arecessed exhaust-tube tube tip formed by the aforementioned method andhaving inexpensive side and end contacts is also disclosed.

BRIEF DESCRIPTION OF THE DRAWING A better understanding of the inventionwill be obtained by referring to the accompanying drawing; wherein:

FIG. 1 is a longitudinal sectional view of a single-ended baselessincandescent lamp incorporating the novel recessed tipoff of the presentinventiom' an'd I l i I FIG. 2 is an enlarged view 6f the basal endportion ofthe lamp illustrating the manner inwhich the exhaust tube istipped off by a beam of infrared 'enr'gy whilethe exhaust tube is stillattached'to the sealex" machine. I

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1 there is shown asingle-ended baseless electric incandescent lamp l0 havinga vitreousenvelope 12 that is terminated by a constrictedfneck portion 13 havingthreads -14 molded on its exterior'surface. The envelope contains afilament 16 of suitable coiled refractory metal wire, such as tu ngsten,which is attached as by clamping or spot welding to the inner ends of apair of lead wires 17,18. The lead wires 17, 18 are hermetically sealedthrough a press 20'formed on the inner end of a vitreous stem tube 21the flared end of which is sealed to the envelope neck 13in thecustomary fashion.

The outer ends of the lead wires 17, 18 extend through the cavity Cdefined by the stem 21 and the outer end of the leadwire 17 is connectedto a disclike contactor member 22 that is cemented or sealed to the endof the envelope neck 13 and closes the stem cavity C. The contactormember 22 can comprise a metal eyelet that is soldered to the lead wire17 so as to provide a centrally located segment 23 that protrudesoutwardly from the eyelet and serves as an end contact for 'the lamp 10.The end of the other lead wire 18 is sealed through a thickened end wallportion 15 of the envelope neck 13 soas to be electrically insulatedfrom the contactor member 22, and the end of this lead is bent aroundthe end portion of the adjacent molded thread 14. A layer 24 ofelectrically conductive material, such as a suitable conductive paint,is applied .over

the exposed end of the lead wire 18 and thus serves as a-side contactfor the lamp l0.

The envelope 12 is evacuated and subsequently charged with an inert gasfill through a vitreous exhaust tube 26 that is sealed to the inner endof the stem 21 and communicates with an aperture 28 provided in the wallof the stem tube just below the stem press 20. After the lamp has beenevacuatedand gasfilled, the exhaust tube 26 is tippedoff at a pointadjacent the inner end of the stem 21 in accordance with the presentinvention-to provide a recessed tip T of fused vitreous material that islocated deep within the stem cavity C.

The tipping-off of the exhaust tube 26 at the aforementioned recessedlocation within the stem cavity C is achieved in accordance with thepresent invention by fabricating the envelope 12 and stem tube 21 from aglass that transmits infrared radiation and by fabricating the exhausttube 26 from a glass which absorbs such radiation.

As a specific example, the envelope 12 and stem tube 21 are composed ofthe customary soda-lead glass (Corning Code No. 0120) customarily usedfor these components. The exhaust tube 26 is composed of a green-coloredpotash-sodalead glass that contains a small'but sufficient amount ofiron oxide to render the glass infrared absorbing. Suchinfrared-absorbing glasses are well known in the art and arecommercially available as Corning Code 9362 and Code 9363 sealingglasses. These sealing glasses have viscosity and expansioncharacteristics that are almost identical with Code 0120 glass and thuspermit the-exhaust tube 26 to be sealed to'the stem tube 21 in thecustomary manner.

Information published by Corning shows that samples of Code 9362 andCode9363 glasses approximately 1 millimeter thick absorb approximatelypercent of infrared energy: in the l to 2 micron wavelength range. Thus,an exhaust tube 26 made of such tipped off can be tipped off within thestem cavity C in a very efficient and convenient manner by focusing abeam of infrared radiation which has the proper wavelength and isgenerated by a source located outside of the lamp being processed. Whilevarious types of infrared-generating sources (such as incandescentradiant-heat coils etc.) may be used, a high-wattage halogen-typeincandescent lamp such as an infrared quartz iodine lamp is preferredsince it has an output which peaks at approximately 1 micron.

As is shown in FIG. 2, the exhaust tube 26 is tipped off while it isstill attached to the compression head 27 of a "sealex" machine whichhas evacuated and charged the envelope 12 with a suitable inert fillgas. At this stage of manufacture, the outer end of the lead wire 18 hasbeen sealed within the end wall [5 of the envelope neck 13 and has beenbent over the adjacent portion of the molded glass thread 14. The end ofthe other lead wire 17 is unattached and merely extends from the stemcavity C on the opposite side of the exhaust tube 26. Tipping-off isaccomplished by positioning a suitable infrared energy source30, such asa pair of 400 watt quartz-iodine lamps, adjacent the envelope neck 13and focusing the infrared radiation, as by a suitable reflector, into aconcentrated beam 31 that passes through the intervening portions of theenvelope neck 13 and stem tube 21 and impinges upon a segment of theexhaust tube 26 that is located deep within the stem cavity C. The beamof infrared energy quickly heat softens the exhaust tube 26 and causesit to collapse inwardly and form a constriction 32, as shown in FIG. 2.The intensity of the infrared energy is such that the exhaust tube 26melts and fonns a fused glass tip T (shown in FIG. 1) which hermeticallycloses off the exhaust tube 26 and the envelope 12 from the atmosphere.

After the tipping-off operation has been completed, the metal contactorplate or eyelet 22 is fastened to the end of the envelope neck 13. thelead wire 17 is trimmed and soldered to the eyelet to provide theprotruding end contact 23, thus completing the fabrication of the lamp10.

While the invention has been illustrated and described in connectionwith an incandescent lamp having a cavity C that is defined by a stemtube 21, the novel tipping-off method can be employed in the manufactureof various types of lamps and devices which are terminated by an endwall which defines a reentrant type cavity through which a vitreousexhaust tube initially extends.

The novel tipping-off method of the present invention facilitates themanufacture of incandescent lamps that are charged with a fill gas (suchas argon, krypton, etc.) to a pressure higher than atmospherio pressure(1 V2 to 2 atmospheres, for example) since it does not require acombustible heat source such as a gas flame. Tipping-off of lamps havingsupraatmospheric fill pressure is readily accomplished by pressurizingthe stem cavity C to prevent the heat-softened segment of the exhausttube 26 from distending and rupturing during the tipping-off operation.This pressurizing can be accomplished by filling the cavity C withcompressed air or other suitable inert gas to a pressure which isapproximately equal to that of the fill gas contained by the envelope 12and conjoined exhaust tube 21. Alternatively, the partly fabricated lampcan be placed within a pressurized enclosure having an infraredradiationtransmitting window through which the beam of infrared energy isdirected onto the recessed segment of the exhaust tube. The infraredsource can also be located within the pressurized enclosure.

It will be appreciated from the foregoing that the objects of theinvention have been achieved in that a very convenient and inexpensivemeans has been provided for tipping-off the exhaust tube of an electriclamp at a location which is recessed within the stem cavity or body ofthe lamp envelope.

While a preferred embodiment has been illustrated and dr scribed. itwill be appreciated that the various modifications can be made withoutdeparting from the spirit and scope of the invention.

lclaim: i

1. In the manufacture of an electric lamp having a vitreous envelopethat is terminated at one end by a reentrant wall that defines a cavityand includes a conjoined vitreous exhaust tube which initially extendsthrough and beyond the cavity and provides a passageway for evacuatingthe envelope and subsequently charging it with a fill gas, the method ofhermetically closing and tipping-off said vitreous exhaust tube at alocation that is recessed within the cavity defined by said reentrantend wall, which method comprises;

fabricating said envelope from a vitreous material that transmitsinfrared radiation; fabricating the conjoined vitreous exhaust tube froma vitreous material that absorbs infrared radiation; and subjecting arecessed segment of said exhaust tube to an externally generated beam ofinfrared radiation thatpasses through the intervening portion of thelamp envelope and is of sufficient intensity that it heat-softens saidtube segment and causes it to collapse into a tip of fused vitreousmaterial that hermetically seals the envelope and terminates the exhausttube.

2. The method of claim 1 wherein;

the reentrant end wall of said envelope comprises a hollow stem that iscomposed of vitreous material that transmits infrared radiation; and

the heat-softening and tipping-off of said recessed segment of theexhaust tube is effected by passing said beam of infrared radiationthrough the intervening portions of said envelope and said vitreousstem.

3. The method of claim 2 wherein:

said envelope is charged to a pressure above atmospheric pressure withan inert fill gas through the exhaust tube prior to the tipping-offthereof; and

the tipping-off of said exhaust tube by said beam of infrared radiationis effected after the stem cavity has been pressurized with an inert gasto a pressure that is substantially equal to the pressure of the fillgas contained by said envelope and conjoined exhaust tube so that theheat-softened recessed segment of the exhaust tube and newly formed tipwill not be distended and ruptured by the supraatmospheric pressureexerted by the contained fill gas.

4. The method of claim 2 wherein:

said beam of infrared radiation is type incandescent lamp; and

the infrared radiation generated by said lamp is focused onto therecessed segment of the exhaust tube which is to be collapsed and tippedoff.

5. A baseless single-ended incandescent lamp comprising:

that contains an envelope of infrared-radiation transmitting glass thatis terminated by a neck portion that has a molded thread formed on itsexterior surface;

a hollow stern of infrared-radiation transmitting glass sealed to saidenvelope neck portion and defining a stem cavity that extends into saidneck portion;

a pair of lead wires sealed through a press formed on the inner end ofsaid stem;

an incandescible filament fastened to the inner ends of said lead wires;

an exhaust tube of infrared-absorbing glass sealed to the inner end ofsaid stem and communicating with an adjacent aperture in the wall ofsaid stem;

said exhaust tube being terminated by a fused hermeticallysealed tipthat is located proximate the inner end of the stem and is thus recessedwithin said stem cavity;

a layer of conductive material overlying at least a part of the threadon said envelope neck portion and constituting a side contact for saidlamp;

a disclike contact member secured to the end of said envelope neckportion and having an outwardly protruding segment that constitutes anend contact for said lamp;

the outer end portion of one of said lead wires being located in thestem cavity and extending through the end of said generated by a halogensaid disclike contact member closes said stem cavity.

8. The incandescent lamp of claim 5 wherein:

said envelope and stem are composed of soda-lead glass;

and i said exhaust tube is composed of potash-soda-lead glass thatcontains an amount of iron oxide such that approximately percentofjinfraredradiation having a wavelength of from 1 to 2 microns isabsorbed by a section of said glass that is approximately 1 millimeterthick.

